There is a demand to further reduce the size and improve the performance of a semiconductor device to be mounted on an electronic apparatus. Along with the reduction in size and improvement in performance of the semiconductor device, many connection terminals have been arranged at a narrow pitch on a lower face or a side face of the semiconductor device, and there has been a demand to achieve more multi-layered and finer (smaller in width) interconnections of a circuit board on which the semiconductor device is to be mounted.
There are various forms of circuit boards on which the semiconductor device is mounted, such as a package board and a silicon interposer. Generally, copper (Cu) or a copper alloy (hereafter, when used alone, the term “copper” is meant to encompass copper alloys) is used as an interconnection material of the circuit boards, since copper and copper alloys have low electrical resistances. Moreover, a subtractive method and a semi-additive method are known as methods of forming copper interconnections in these circuit boards. It is said that the semi-addictive method is better suited than the subtractive method for forming the copper interconnections at a narrow pitch of the package board, the silicon interposer, and the like.
Patent Document 1: Japanese Laid-open Patent Publication No. 2004-304167
Patent Document 2: Japanese Laid-open Patent Publication No. 2004-14975
Patent Document 3: Japanese Laid-open Patent Publication No. 2008-34639
Patent Document 4: Japanese Laid-open Patent Publication No. 2003-124591
When copper is used as the interconnection material, Cu atoms sometimes diffuse into an insulating film covering the interconnections. Thus, a leakage between the interconnections becomes a problem along with the finer designing of interconnection. Moreover, there is a problem that the surfaces of copper interconnections are oxidized by moisture and oxygen contained in the insulating film thereby causing an increase in interconnection resistance. Furthermore, the finer designing of the interconnections causes a phenomenon in which metal atoms move along with the electric conduction and the width of each interconnection becomes even smaller, i.e. electromigration. Hence, the reliability in a long-term use is reduced. Although the copper interconnections have a higher electromigration resistance than aluminum interconnections, the electromigration may not be ignored when the width of the copper interconnections is, for example, 2 μm or less.